Funding is requested for the purchase of a Bruker ESP 300 Spectrometer system as part of a Shared Instrumentation Facility at the Johns Hopkins University School of Medicine. Purchase of this spectrometer will enable the creation of a facility for the performance of multifrequency EPR experiments. This instrumentation will serve seven major user projects in the areas of Cardiology, Oncology, Pulmonary Research, and Toxicology. These projects all require the use of an X-Band, Q-Band, S-Band or L-Band spectrometer. Critical need for this instrumentation arises from the extremely limited amount of spectrometer time available on the one IBM-Bruker ER 300 instrument now in operation at the Johns Hopkins University School of Medicine. This one instrument is presently shared for X-Band, Q-Band, S-Band and L-Band measurements of both invitro and in vivo systems. The current lack of accessibility to this instrumentation throughout the institution threatens to impede the progress of each of the major user projects, all of which are currently funded by NIH awards. The Bruker ESP 300 Spectrometer system requested is ideally suited to performing the in vivo and in vitro applications described in the proposal. It is fully compatible with the existing Q-Band, L-Band and S-Band microwave bridges currently available in the EPR Laboratories at the Johns Hopkins University School of Medicine. These bridges will be used along with the Bruker 300 ESP X-Band commercial EPR system to enable the performance of high quality EPR measurements at frequencies ranging from 1 GHz up to 35 GHz.